Install Playwright to control Firefox

[Playwright] is a cross-browser automation framework, intended for
automating browser-based GUI application tests.  It also works as a
general remote-control tool for automating basically anything having to
do with a browser.

Playwright requires a special Firefox binary that it manages itself.  To
avoid downloading and installing Playwright and Firefox, and thus
storing them in memory, we need them to be already available in the
rootfs image.  Since I want the control software to be updated easily,
without rebooting the machine, I decided to separate it into its own
project, [Voonex].  A short shell script to install/update and run it is
launched by the systemd user instance.

[Playwright]: https://playwright.dev/
[Voonex]: https://git.pyrocufflink.blue/dustin/voonex

overlay/etc/systemd/system/xinit@.service

@@ -14,7 +14,7 @@ TTYPath=/dev/tty7
 StandardInput=tty
 StandardOutput=journal
 StandardError=journal
-ExecStart=/usr/bin/startx
+ExecStart=/usr/bin/startx -- -nocursor
 Restart=always
 
 [Install]